Gravity drop hammers, such as described in the applicant's own prior patent applications PCT/NZ93/00074 and PCT/NZ2006/000117 are primarily utilised for breaking exposed surface rock. These hammers generally consist of a striker pin which extends outside a nose piece positioned at the end of a housing which contains a heavy moveable mass. In use, the lower end of the striker pin is placed on a rock and the moveable mass subsequently allowed to fall under gravity from a raised position to impact onto the upper end of the striker pin, which in turn transfers the impact forces to the rock.
Elevated stress levels are generated throughout the entire hammer apparatus and associated supporting machinery (e.g. an excavator, known as the carrier) by the high impact forces associated with such breaking actions. PCT/NZ93/00074 discloses an apparatus for mitigating the impact forces from such operations by using a unitary shock absorbing means in conjunction with a retainer supporting a striker pin within the nose piece.
The unitary shock absorbing means is a block of at least partially elastic material which compresses under the impact force of the moveable mass on the striker pin. The striker pin attachment to the nose piece is configured with a small degree of allowable travel constrained by a pair of retaining pins fitted to the retainer and allowing movement along the longitudinal striker pin axis via recesses formed into the sides of the striker pin.
Despite the advantages of the system described in PCT/NZ93/00074, there is an ongoing desire to further attenuate the effects of impact forces on the device and/or reducing the device weight, to allow the use of a smaller carrier. Such improvements also result in reduction in wear and associated maintenance requirements.
All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.
It is acknowledged that the term ‘comprise’ may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term ‘comprise’ shall have an inclusive meaning—i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term ‘comprised’ or ‘comprising’ is used in relation to one or more steps in a method or process.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.